Compositions and methods for tissue repair with extracellular matrices

ABSTRACT

Described herein are compositions comprising decellularized extracellular matrix derived from skeletal muscle or other suitable tissue, and therapeutic uses thereof. Methods for treating, repairing or regenerating defective, diseased, damage, ischemic, ulcer cells, tissues or organs in a subject preferably a human, with diseases, such as PAD and CLI, using a decellularized extracellular matrix of the invention are provided. Methods of preparing culture surfaces and culturing cells with absorbed decellularized extracellular matrix are provided.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of PCT Application No. PCT/US2012/054058 which claims priority to U.S. Provisional Application No. 61/531,931, filed Sep. 7, 2011, the entire contents of which are incorporated by reference herewith.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under grant No. OD004309 awarded by National Institutes of Health (NIH). The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Peripheral artery disease (PAD) is a common condition in which blood flow is reduced to the limbs, typically the leg and feet (Manzi et al., 2011; Stansby and Williams, 2011), and if untreated, may progress to the stage of critical limb ischemia (CLI), which is the most advanced form of PAD often leading to amputation of the limb and potential mortality (Chan and Cheng, 2011; Dattilo and Casserly, 2011). Similar to myocardial infarction (MI), which is also a result of atherosclerosis, PAD has a large population of affected individuals, with an estimated 27 million suffering from PAD in Europe and North America (Belch et al., 2003). Despite recent medical advances and the advent of tissue engineering strategies, revascularization through surgical or endovascular intervention, remains the only treatment. This is further complicated by the fact that approximately 40% of patients with critical limb ischemia (CLI) are not candidates for revascularization procedures (Sprengers et al., 2008), and that revascularization has limited benefit when the PAD is diffuse or below the knee. This corresponds to approximately 120,000 leg amputations in the US and 100,000 in the European Union each year (Lawall et al., 2010). There is therefore a pressing need for the development of new therapies for treating PAD and CLI.

Alternative therapies for PAD and CLI have largely mirrored the attempts for MI and heart failure, including cell transplantation and angiogenic growth factor therapy (Fadini et al., 2010; Menasche, 2010; Tongers et al., 2008). The goal of these therapies has been to increase vascularization of the ischemic limb so that perfusion is sufficient for wound healing to occur, and to resolve pain at rest, thereby also preventing limb amputations. Biomaterial based strategies have recently been explored. Currently, only poly(d,l-lactide-co-glycolide) (PLGA), collagen-fibronectin, alginate, gelatin, fibrin, and peptide amphiphiles have been examined (Doi et al., 2007; Jay et al., 2008; Kong et al., 2008; Layman et al., 2007; Lee et al., 2010; Ruvinov et al., 2010; Silva and Mooney, 2007; Webber et al., 2011). PLGA microspheres in alginate hydrogels have been utilized to deliver vascular endothelial growth factor (VEGF) (Lee et al., 2010), and alginate hydrogels have been explored for delivery of hepatocyte growth factor (HGF) (Ruvinov et al., 2010), VEGF (Silva and Mooney, 2007), and pDNA encoding for VEGF (Kong et al., 2008). Alginate microspheres within an injectable collagen matrix have also been used to deliver stromal cell-derived factor-1 (SDF-1) (Kuraitis et al., 2011), while VEGF loaded alginate microparticles in a collagen-fibronectin scaffold were used to deliver endothelial cells (Jay et al., 2008). Gelatin hydrogels have been employed to deliver basic fibroblast growth factor (bFGF) (Doi et al., 2007; Layman et al., 2007), and fibrin scaffolds were utilized to deliver bFGF and granulocyte-colony stimulating factor (G-CSF) along with bone marrow cells. More recently, VEGF-mimetic peptides were delivered using assembling peptide amphiphiles (Webber et al., 2011). Each of these studies demonstrated enhanced cell transplantation and/or enhanced growth factor/gene delivery with resulting enhancements in neovascularization.

While each of the materials currently explored for treating PAD have been used extensively as tissue engineering scaffolds, they do not mimic the extracellular microenvironment of the skeletal muscle they are intended to treat.

Recently, several clinical trials using cell therapy have demonstrated promising results (Alev et al., 2011; Gupta and Losordo, 2011; Kawamoto et al., 2009; Menasche, 2010), but there are still many questions about which therapeutic cell type to use, quantity of cells, and best route to deliver the cells, as well as a significant problem with poor cell retention and survival (Menasché, 2010). Biomaterial scaffolds have more recently been explored to enhance cell survival by providing a temporary mimic of the extracellular matrix (ECM) (Kawamoto et al., 2009; Layman et al., 2011). Biomaterials have also been used for delivery of growth factors or their mimics in animal models of PAD and CLI (Kawamoto et al., 2009; Layman et al., 2011; Ruvinov et al., 2010; Webber et al., 2011). However, these scaffolds are composed of fibrin (Layman et al., 2011), collagen-based matrix (Kuraitis et al., 2011), gelatin (Layman et al., 2007), self-assembling peptide amphiphiles (Webber et al., 2011) or alginate (Ruvinov et al., 2010), which may not provide the proper biomimetic environment for the ischemic skeletal muscle in these conditions. Moreover, no potential therapies employing only a biomaterial have been explored to date. An acellular, biomaterial only approach may reach the clinic sooner since it has the potential to be an off-the-shelf treatment and does not have the added complications that cells bring, including appropriate source, the need for expansion, or potential disease transmission. Furthermore, a biomaterial that promotes neovascularization and tissue repair on its own would obviate the need for exogenous growth factors, and the difficulties and expense associated with such a combination product.

The extracellular matrix (ECM) of each tissue contains similar components; however, each individual tissue is composed of a unique combination of proteins and proteoglycans (Lutolf and Hubbell, 2005; Uriel et al., 2009). Recent studies have shown that the ECM of various tissues can be isolated through decellularization and utilized as a tissue engineering scaffold (Merritt et al.; Ott et al., 2008; Singelyn et al., 2009; Uygun et al., 2010; Valentin et al., 2010; Young et al., 2011). Other decellularized ECM materials have been used for a variety of applications for tissue repair (Crapo et al., 2011; Gilbert et al., 2006). These scaffolds are known to promote cellular influx in a variety of tissues (Numata et al., 2004; Rieder et al., 2006). Their degradation products have angiogenic (Li et al., 2004) and chemoattractant (Badylak et al., 2001; Beattie et al., 2008; Li et al., 2004; Zantop et al., 2006) properties, and also promote cell migration and proliferation (Reing et al., 2009). After removal of the cellular antigens, these scaffolds are considered biocompatible, and both allogeneic and xenogeneic ECM devices have been approved by the FDA and are in clinical use (Badylak, 2007).

Hydrogels derived from decellularized ECMs, including myocardium (Singelyn et al., 2009), pericardium (Seif-Naraghi et al., 2010), and adipose tissue (Young et al., 2011), were recently developed which assemble into porous and fibrous scaffolds upon injection in vivo. It is also recently shown that the injectable hydrogel derived from ventricular ECM promoted endogenous cardiomyocyte survival and preserved cardiac function post-myocardial infarction (Singelyn et al., 2012).

Skeletal muscles are composed of bundles of highly oriented and dense muscle fibers, each a multinucleated cell derived from myoblasts. The muscle fibers in native skeletal muscle are closely packed together in an extracellular three-dimensional matrix to form an organized tissue with high cell density and cellular orientation to generate longitudinal contraction. Skeletal muscle can develop scar tissue after injury which leads to a loss of functionality. The engineering of muscle tissue in vitro holds promise for the treatment of skeletal muscle defects as an alternative to host muscle transfer. Tissue engineering compositions must be biocompatible and capable of being vascularised and innervated.

The reconstruction of skeletal muscle, which is lost by injury, tumor resection, or various myopathies, is limited by the lack of functional substitutes. Surgical treatments, such as muscle transplantation and transposition techniques, have had some success; however, there still exists a need for alternative therapies. Tissue engineering approaches offer potential new solutions; however, current options offer incomplete regeneration. Many naturally derived as well as synthetic materials have been explored as scaffolds for skeletal tissue engineering, but none offer a complex mimic of the native skeletal extracellular matrix, which possesses important cues for cell survival, differentiation, and migration.

The extracellular matrix consists of a complex tissue-specific network of proteins and polysaccharides, which help regulate cell growth, survival and differentiation. Despite the complex nature of native ECM, in vitro cell studies traditionally assess cell behavior on single ECM component coatings, thus posing limitations on translating findings from in vitro cell studies to the in vivo setting. Overcoming this limitation is important for cell-mediated therapies, which rely on cultured and expanded cells retaining native cell behavior over time.

Typically, purified matrix proteins from various animal sources are adsorbed to cell culture substrates to provide a protein substrate for cell attachment and to modify cellular behavior. However, these approaches would not provide an accurate representation of the complex microenvironment. More complex coatings have been used, such as a combination of single proteins, and while these combinatorial signals have shown to affect cell behavior, it is not as complete as in vivo. For a more natural matrix, cell-derived matrices have been used. Matrigel is a complex system; however, it is derived from mouse sarcoma, and does not mimic any natural tissue. While many components of ECM are similar, each tissue or organ has a unique composition, and a tissue specific naturally derived source may prove to be a better mimic of the cell microenvironment.

A liquid form of skeletal muscle matrix was shown to promote the differentiation and maturation of C2C12 skeletal myoblast progenitors when used as a cell culture coating due to its ability to retain a complex mixture of skeletal muscle ECM proteins, peptides, and proteoglycans (DeQuach et al., 2010). A decellularized skeletal muscle scaffold has been previously explored for replacement of a muscle defect (Merritt et al.; Wolf et al., 2012), yet this intact scaffold would not be amenable to treating certain non-skeletal muscle tissue disease, such as the peripheral artery disease (PAD) and CLI.

As discussed above, the only current clinical treatment for PAD and CLI is endovascular or surgical revascularization (Dattilo and Casserly, 2011). Surgical bypass was the established standard, but recently endovascular therapies such as angioplasty, atherectomy and stenting are used as less-invasive options. However, despite these therapies, CLI continues to carry a major risk of limb amputation, with rates that have not changed significantly in 30 years (Tongers et al., 2008). Unfortunately, few therapies exist for treating the ischemic skeletal muscle in these conditions. Biomaterials have been used to increase cell transplant survival as well as deliver growth factors to treat limb ischemia; however, existing materials do not mimic the native skeletal muscle microenvironment they are intended to treat. Furthermore, no therapies involving biomaterials alone have been examined.

SUMMARY OF THE INVENTION

The present invention provides biomaterials comprising extracellular matrix (ECM) derived from skeletal muscle or other suitable tissue, and method of use thereof, for therapeutic treatment of ischemia, ulcer, and/or other damages in certain diseases. In certain embodiments, the present invention provides injectable biomaterials comprising skeletal muscle extracellular matrix, and method of use thereof, for treating peripheral artery disease (PAD), critical limb ischemia (CLI), and symptoms and associated complications with these diseases, as well as pressure ulcers, venous ulcers, diabetic ulcers, chronic vascular ulcers, tunneled/undermined wounds, surgical wounds (donor sites/grafts, post-Mohs surgery, post-laser surgery, podiatric, wound dehiscence), trauma wounds (abrasions, lacerations, second-degree burns and skin tears), draining wounds, inflammation, Buerger disease, atherosclerosis obliterans, and thromboangiitis obliterans, and gangrene.

In certain embodiments, the present invention provides compositions and methods comprising injecting or implanting in a subject with PAD and/or CLI in need an effective amount of a composition comprising decellularized extracellular matrix derived from skeletal muscle tissue. In other embodiments, the present invention provides a method comprising injecting or implanting in a subject with PAD and/or CLI in need a composition comprising decellularized extracellular matrix derived from a suitable tissue, including but not limited to, cardiac, pericardial, liver, brain, small intestine submucosa, bladder, lung, and vascular tissue. In certain embodiments, the injection or implantation of said composition repairs damage to skeletal muscle tissue sustained by said subject. In other embodiments, the injection or implantation of said composition repairs damage caused by ischemia in said subject. The composition of the present invention comprising the ECM material can degrade within about one month, two months, or three months following injection or implantation. In certain embodiments, the injection or implantation of said composition repairs damage to skeletal muscle tissue sustained by said subject. In certain embodiments, the injection or implantation of said composition repairs damage caused by ischemia in said subject. Herein, said effective amount can be an amount that increases blood flow in the area of the injection or implantation or treated limb of the treated subject. In some instances the effective amount is an amount that increases the Ankle-Brachial Index of the treated subject. In some instances the effective amount is an amount that increases blood flow as measured by Doppler waveform analysis, pulse volume recording, duplex arterial ultrasound study, or exercise Doppler stress testing. In some instances, the effective amount is an amount that increases muscle mass in the area of the injection or implantation or treated limb of the treated subject. In some instances, the effective amount is an amount that induces new vascular formation in the area of the injection or implantation of the treated subject. The present invention provides that a liquid form of skeletal muscle matrix can assemble into a fibrous scaffold upon injection in vivo. The material can also be processed into a lyophilized form that only requires sterile water, PBS, or saline to resuspend prior to injection, which can provide ease of storage and use in a clinical setting. The injectable skeletal muscle material of the present invention promotes proliferation of vascular cells and muscle progenitors in vitro, and that the hydrogel enhances neovascularization as well as the infiltration of muscle progenitors and proliferating muscle cells in vivo in a hindlimb ischemia model, thereby demonstrating its capability for treating PAD and CLI by not only treating ischemia, but also promoting tissue repair. The composition can further comprise cells, drugs, proteins, or polysaccharides. In some instances, the composition is coated on a device such as an implant. The composition can be delivered as a liquid, and in many instances, the composition can transition to a gel form after delivery. In certain embodiments, the composition is delivered as a powder.

In one aspect, the invention provides a composition comprising decellularized extracellular matrix derived from skeletal muscle tissue or other suitable tissues. The composition can be injectable. The composition can be formulated into a powder or particulate. In other instances, the composition can be formulated to be in liquid form at room temperature, typically 20° C. to 25° C., and in gel form at a temperature greater than room temperature or greater than 35° C. In some instances, the composition is configured to be delivered to a tissue parenterally, such as through a small gauge needle (e.g., 27 gauge or smaller). In some instances, said composition is suitable for direct implantation into a patient. The composition can be formulated either in a dry or hydrated form to be placed on or in wounds.

In some instances the composition comprises native proteins. In some instances the composition comprises native peptides. In some instances the composition comprises native glycosaminoglycans. In some instances, the composition further comprises non-naturally occurring factors that recruit cells into the composition, encourage growth or prevent infection. In some embodiments, the composition comprising decellularized extracellular matrix derived from skeletal muscle tissue herein retains native glycosaminoglycans. In some instances, the composition comprises naturally occurring factors that recruit cells into the composition, encourage growth or prevent infection.

In some instances, the composition further comprises a population of exogenous or autologous therapeutic cells. The cells can be stem cells or other precursors of skeletal muscle cells or other cell types.

In some instances, the composition further comprises a therapeutic agent, and as such is configured as a drug delivery vehicle. In some instances, the composition is configured to coat surfaces, such as tissue culture plates or scaffolds, to culture skeletal muscle, skeletal muscle cells, or other cell types relevant to skeletal muscle repair.

In an aspect, a method of producing a composition is disclosed herein that comprises decellularized skeletal muscle or other tissue extracellular matrix comprising: obtaining from a subject a skeletal muscle or other suitable tissue sample having an extracellular matrix and non-extracellular matrix components; processing skeletal muscle or other tissue sample to remove the non-extracellular matrix component to obtain decellularized skeletal muscle or other tissue extracellular matrix and extracellular proteins and polysaccharides; and sterilizing the decellularized skeletal muscle or other tissue extracellular matrix. In some instances, said method is performed aseptically without sterilization. In some instances, said method further comprises the step of lyophilizing and grinding up the decellularized skeletal muscle or other tissue extracellular matrix. In some instances, said method further comprises the step of enzymatically treating, solubilizing, or suspending the decellularized skeletal muscle or other tissue extracellular matrix. In some instances, said decellularized skeletal muscle or other tissue extracellular matrix is digested with pepsin at a low pH.

In some instances, said method further comprises the step of suspending and neutralizing said decellularized skeletal muscle or other tissue extracellular matrix in a solution. In some instances, said solution is a phosphate buffered solution (PBS) or saline solution which can be injected through a high gauge needle into the desired tissue or organ. In some instances, said composition is formed into a gel at body temperature. In some instances, said composition further comprises cells, drugs, proteins or other therapeutic agents that can be delivered within or attached to the composition before, during or after gelation.

In some instances, said solution is placed into tissue culture plates or wells, incubated at above 35° C. or about 37° C. to form into a gel that is used for cell culture. In one aspect, the invention provides a method of culturing cells on an adsorbed matrix comprising the steps of: providing a solution comprising decellularized extracellular matrix derived from skeletal muscle or other suitable tissues into a tissue culture device; incubating said tissue culture plates device; removing said solution; and culturing cells on the adsorbed matrix. In some instances, said cells are skeletal muscle cells or other cell types relevant to skeletal muscle or other tissue repair.

In an aspect, a method of culturing cells on an adsorbed matrix comprises the steps of: providing a solution comprising decellularized extracellular matrix derived from skeletal muscle or other suitable tissues into a tissue culture device; incubating said tissue culture plates device; removing said solution; and culturing cells on the adsorbed matrix. In some instances, said cells are skeletal myoblasts, stem cells or other cell types relevant to skeletal muscle repair.

In one aspect, the invention provides a therapeutic method for skeletal muscle and/or other tissue (such as ischemic tissue, or ulcer tissue) repair in a subject comprising injecting or implanting a therapeutically effective amount of a composition comprising decellularized extracellular matrix derived from skeletal muscle or other suitable tissue into a subject in need thereof. In an aspect, a therapeutic method for skeletal muscle or other tissue repair in a subject comprises implanting a composition comprising decellularized extracellular matrix derived from skeletal muscle or other suitable tissues.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates decellularization and tissue processing. FIG. 1(A) shows decellularized skeletal muscle matrix. FIG. 1(B) shows lyophilized skeletal muscle matrix prior to milling. FIG. 1(C) shows digested skeletal muscle matrix. FIG. 1(D) shows in vitro gel of the skeletal muscle matrix with media on top in right well. FIG. 1(E) shows that skeletal muscle matrix that has been digested and re-lyophilized. FIG. 1(F) shows re-lyophilized skeletal muscle matrix resuspended using only sterile water.

FIG. 2 illustrates in vitro mitogenic activity assay. FIG. 2(A) shows rat aortic smooth muscle cells and FIG. 2(B) shows that C2C12 skeletal myoblasts were cultured using growth media with the addition of degraded skeletal muscle matrix, collagen, or pepsin. Proliferation rate was increased for both cell types when cultured in the presence of skeletal muscle matrix degradation products.

FIG. 3 illustrates Rheological data. A representative trace of the storage (G′) and loss (G″) moduli for the skeletal muscle matrix gel is shown.

FIG. 4 illustrates skeletal muscle matrix delivery and gelation in situ. FIG. 4(A) shows intramuscular injection of the skeletal muscle matrix material. FIG. 4(B) shows gelation of the skeletal muscle matrix in situ after 20 minutes as seen after excision of the muscle; arrow denotes the white matrix. FIG. 4(C) shows DAB staining of the biotin-labeled skeletal muscle matrix that gelled within the muscle. Scale bar at 200 μm.

FIG. 5 illustrates scanning electron microscopy. Micrograph of a cross-section of skeletal muscle matrix formed FIG. 5(A) in vitro, and FIG. 5(B) 20 minutes post-subcutaneous injection. Note the formation of the assembled fibers on the nano- and micro-scale. Scale bar at 100 μm.

FIG. 6 illustrates quantification of arterioles. FIG. 6(A) shows collagen and FIG. 6(B) shows skeletal muscle matrix injection regions stained with anti-alpha-SMA (red greyscale) to determine arteriole formation. Vessels with a clear lumen are seen within the injection region at 5 days. Scale bar at 100 μm. Quantification of the vessel density at 3, 5, 7, and 14 days for vessels with a lumen FIG. 6(C)>10 μm or FIG. 6(D)>25 μm demonstrated that the skeletal muscle matrix increased neovascularization. Vessels were, on average, larger in the skeletal muscle matrix when compared to collagen.

FIG. 7 illustrates quantification of endothelial cell recruitment. FIG. 7(A) shows collagen and FIG. 7(B) shows skeletal muscle matrix injection regions stained with isolectin (green greyscale) to assess endothelial cell infiltration at 5 days. Scale bar at 100 μm.* and dotted line denote area of material. FIG. 7(C) shows that endothelial cell infiltration at 3, 5, 7, and 14 days was similar across all four time points, but was significantly greater in the skeletal muscle matrix injection region at 3 and 7 days post-injection.

FIG. 8 illustrates proliferating muscle cell recruitment. FIG. 8(A) shows collagen injection region and FIG. 8(B) shows skeletal muscle matrix injection region at 5 days with desmin-stained cells (green greyscale) co-labeled with Ki67 (red greyscale). Arrows denote desmin and Ki67 positive cells. Scale bar at 20 μm. Insert shows positive desmin staining of healthy skeletal muscle, scale bar at 100 μm. FIG. 8(C) shows quantification of desmin-positive cells in the skeletal muscle matrix compared to collagen normalized to area. Note that there are significantly more desmin-positive cells in the skeletal muscle matrix. FIG. 8(D) shows that, of these desmin-positive cells, a majority of the cells are proliferating as seen by Ki67 co-labeling.

FIG. 9 illustrates muscle progenitor infiltration. MyoD positive cells (green greyscale) in FIG. 9(A) collagen and FIG. 9(B) skeletal muscle matrix injection regions at 5 days. Area of injection is denoted by the dotted line. Scale bar at 20 μm. FIG. 9(C) shows graph of MyoD-positive cells normalized to the area for the injection region. The number of MyoD-positive cells was significantly higher in the skeletal muscle matrix regions at all time points.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a decellularized skeletal muscle extracellular matrix (ECM) composition, and method of use thereof, for treating ischemia, ulcer, and other tissue damage, as well as for restoring muscle mass and function in certain diseases. Described herein are compositions comprising ECM derived from skeletal muscle tissue or other suitable tissues, including, but not limited to, cardiac, pericardial, liver, brain, small intestine submucosa, bladder, lung, and vascular tissue, which can be used for injection into skeletal muscle tissue and/or other tissues in need of therapeutic treatment. In certain embodiments, the ECM composition of the present invention can also be used to support injured tissue or change the mechanical properties. In certain embodiments, the ECM composition as described herein can help regenerate defective or absent skeletal muscle and restore muscle mass and function. In certain embodiments, the injection or implantation of said composition repairs damage to skeletal muscle tissue sustained by said subject.

In certain embodiments, the present invention provides a decellularized skeletal muscle extracellular matrix (ECM) composition, and method of use thereof, for treating peripheral artery disease (PAD) and critical limb ischemia (CLI). The present invention provides that the decellularized skeletal muscle extracellular matrix composition of the present invention increases arteriole and capillary density, as well as recruited more desmin-positive and MyoD-positive cells compared to collagen, indicating that the tissue specific decellularized skeletal muscle extracellular matrix composition which can be formed in an injectable hydrogel is a therapy for treating ischemia related to PAD, as well as beneficial effects on restoring muscle mass that is typically lost in critical limb ischemia (CLI). In other embodiments, the injection or implantation of said composition repairs damage caused by ischemia in said subject. The composition of the present invention comprising the ECM derived from skeletal muscle or other suitable tissues as discussed herein degrades within about one month, two months, or three months following injection or implantation.

In certain embodiments, the present invention further provides a decellularized skeletal muscle extracellular matrix (ECM) composition, and method of use thereof, for treating other diseases resulting from ischemia, ulcer, muscle mass lost, or other tissue damage. Exemplary diseases that can be treated using the decellularized skeletal muscle extracellular matrix (ECM) composition of the present invention include, but are not limited to pressure ulcers, venous ulcers, diabetic ulcers, chronic vascular ulcers, tunneled/undermined wounds, surgical wounds (donor sites/grafts, post-Mohs surgery, post-laser surgery, podiatric, wound dehiscence), trauma wounds (abrasions, lacerations, second-degree burns and skin tears), draining wounds, inflammation, Buerger disease, atherosclerosis obliterans, and thromboangiitis obliterans, and gangrene.

The present invention further provides a method of delivering the decellularized skeletal muscle extracellular matrix (ECM) composition of the present invention, with or without other therapeutic agents, including cells, into one or more injured tissues or organs damaged by certain disease conditions or trauma. In some instances, methods of delivery are described wherein the skeletal muscle ECM composition of the present invention can be placed in contact with a defective, diseased or absent muscle tissues or other injured tissues, resulting in skeletal muscle tissue regeneration and restoration of muscle mass and function. Exemplary methods for delivery of a composition comprising the skeletal muscle ECM include, but are not limited to: direct instillation during surgery; direct injection into the injured tissue or organ; indirect delivery through a catheter to the injured tissue or organ. The composition can also be delivered as a liquid, gel or in a solid formulation, such as a graft or patch or associated with a cellular scaffold or a particulate. Dosages and frequency will vary depending upon the needs of the patient and judgment of the physician.

In certain embodiments, the present invention provides a native skeletal muscle ECM decellularization and gelation method to create an in situ scaffold for cellular transplantation. An appropriate digestion and preparation protocol has been provided herein that can create nanofibrous gels. The gel solution is capable of being parenterally delivered into the skeletal muscle tissue or other injured tissue or organ, thus providing an in situ gelling scaffold. Since a decellularized skeletal muscle ECM best mimics the natural skeletal muscle environment, it improves cell survival and retention upon injection at the site of the injured tissue, thus encouraging tissue regeneration.

The skeletal muscle ECM of the present invention can also be used to recruit cells into the injured tissue or as a drug delivery vehicle. In some instances, the composition herein can recruit endogenous cells within the recipient and can coordinate the function of the newly recruited or added cells, allowing for cell proliferation or migration within the composition. An extracellular matrix composition herein can further comprise one or more additional components, for example without limitation: an exogenous cell, a peptide, polypeptide, or protein, a vector expressing a DNA of a bioactive molecule, and other therapeutic agents such as drugs, cellular growth factors, nutrients, antibiotics or other bioactive molecules. Therefore, in certain preferred embodiments, the ECM composition can further comprise an exogenous population of cells such as stem cells or progenitor, or skeletal muscle cell precursors, as described below.

The skeletal muscle ECM of the present invention can be derived from the native or natural matrix of mammalian skeletal muscle tissue. The skeletal muscle ECM of the present invention can also be derived from an animal or synthetic source. In some instances, the decellularized skeletal muscle extracellular matrix is derived from native skeletal muscle tissue selected from the group consisting of human, porcine, bovine, goat, mouse, rat, rabbit, or any other mammalian or animal skeletal muscle. In some embodiments, the biocompatible composition comprising the decellularized skeletal muscle extracellular matrix is in an injectable gel or solution form, and can be used for skeletal muscle or other tissue repair by transplanting or delivering cells contained therein into the injured or desired tissue in need following a disease condition, or recruiting the patient's own cells into the injured or desired tissue in need. In other instances, the biocompatible material comprising a decellularized skeletal ECM is, for example, a patch, an emulsion, a viscous liquid, fragments, particles, microbeads, or nanobeads.

In some instances, the invention provides biocompatible materials for culturing skeletal muscle cells or other skeletal muscle relevant cells in research laboratories, or in a clinical setting prior to transplantation and for skeletal muscle or other tissue repair. Methods for manufacturing and coating a surface, such as tissue culture plates or wells, with decellularized skeletal extracellular matrix are also provided. The biocompatible materials of the invention are also suitable for implantation into a patient, whether human or animal.

The invention further provides a method of producing a biocompatible material comprising the decellularized skeletal muscle extracellular matrix of the invention. Such method comprises the steps of: (a) obtaining a skeletal muscle tissue sample having an extracellular matrix component and non-extracellular matrix component; (b) processing the skeletal muscle tissue sample to remove at least a portion or substantially all the non-extracellular matrix component to obtain decellularized skeletal muscle extracellular matrix; and (c) sterilizing the decellularized skeletal muscle extracellular matrix. In certain embodiments, the skeletal muscle tissue sample is isolated from a mammal such as a non-primate (e.g., cows, pigs, horses, cats, dogs, rats, etc.) or a primate (e.g., monkey and human), or an avian source (e.g., chicken, duck, etc.). Decellularization procedures for the skeletal tissue sample are performed using one or more physical, chemical and/or biological techniques, known in the art and as taught herein. Methods of making the compositions herein can include decellularizing tissue from any age animal or human by methods well known in the art.

For human therapy, there are many potential sources for the skeletal muscle extracellular matrix material: human skeletal muscle (including autologous, allogeneic, or cadaveric), porcine skeletal muscle, bovine skeletal muscle, goat skeletal muscle, mouse skeletal muscle, rat skeletal muscle, rabbit skeletal muscle, chicken skeletal muscle, and other animal sources. One donor skeletal muscle can be used to treat many people. Non-human animals are a source of skeletal muscle extracellular matrix without the need for human donors. As a research reagent, non-human animal sources can be utilized.

In certain embodiments, the method of processing the skeletal muscle extracellular matrix is as follows. The skeletal tissue is first decellularized, leaving only the extracellular matrix. Decellularization can be performed with a perfusion of sodium dodecyl sulfate and phosphate buffered solution, or other detergents, for example. The skeletal muscle extracellular matrix is then lyophilized, ground up, and digested with pepsin at a low pH, between about pH 1-6 or pH 1-4, or other matrix degrading enzymes such as matrix metalloproteinases.

To produce a gel form of the skeletal muscle extracellular matrix for in vivo therapy, the solution comprising the skeletal muscle extracellular matrix is then neutralized and brought up to the desired temperature, concentration and viscosity using PBS/saline. In certain embodiments, the ECM concentration can be 1-20 mg/mL, or 2-8 mg/mL. The solution comprising the skeletal muscle extracellular matrix can then be injected through a high gauge needle, such as 27 gauge or higher, into the injured tissue or any tissue in need. At body temperature, e.g., 36.8° C.±0.7° C., such solution then forms into a gel. Cells, drugs, proteins, or other therapeutic agents can also be delivered inside the skeletal muscle ECM gel.

To produce a gel form of the skeletal muscle extracellular matrix for in vitro uses, the solution comprising the skeletal muscle extracellular matrix is neutralized and brought up to the desired concentration using PBS/saline. In certain embodiments, the ECM concentration can be 1-20 mg/mL, or 2-8 mg/mL. Such solution can then be placed onto any solid surface such as into tissue culture plates/wells. Once placed in an incubator at 37° C. or above room temperature, the solution forms a gel that can be used for cell culture.

The invention also provides a therapeutic method for skeletal muscle or other relevant tissue repair in a subject comprising injecting or implanting in part or in its entirety the biocompatible skeletal muscle ECM material of the invention into a patient. The invention further provides a therapeutic method for treating PDA, CLI, or other defective, diseased, damaged, ischemic, ulcer, or other injured tissue or organ in a subject comprising injecting or implanting the biocompatible material of the invention in situ.

The compositions herein can comprise a decellularized ECM derived from skeletal muscle tissue and another component or components. In some instances, the amount of ECM in the total composition is greater than 90% or 95% or 99% of the composition by weight. In some embodiments, the ECM in the total composition is greater than 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or 80% of the composition by weight.

Decellularized extracellular matrices are prepared such that much of the bioactivity for skeletal muscle tissue regeneration is preserved. Exemplary bioactivity of the compositions herein include without limitation: control or initiation of cell adhesion, cell migration, cell differentiation, cell maturation, cell organization, cell proliferation, cell death (apoptosis), stimulation of angiogenesis, proteolytic activity, enzymatic activity, cell motility, protein and cell modulation, activation of transcriptional events, provision for translation events, inhibition of some bioactivities, for example inhibition of coagulation, stem cell attraction, chemotaxis, and MMP or other enzyme activity.

The compositions comprise an extracellular matrix that is substantially decellularized. In some instances, a decellularized matrix comprises no living native cells with which the ECM naturally occurs. In some instances, a substantially decellularized matrix comprises less than 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10% native cells by weight.

As described herein, a composition can comprise a decellularized skeletal muscle ECM and different tissue decellularized EMC or a synthetic or naturally occurring polymer from animal and non-animal sources (such as plants or synthetic collagens). For example, a composition herein comprises a natural polymer such as collagen, chitosan, alginate, glycosaminoglycans, fibrin, or hyaluronic acid. In another example, a composition herein comprises a synthetic polymer, for example without limitation, polyethylene glycol, poly(glycolic)acid, poly(lactic acid), poly(hydroxy acids), polydioxanone, polycaprolactone, poly(ortho esters), poly(anhydrides), polyphosphazenes, poly(amino acids), pseudo-poly(amino acids), conductive polymers (such as polyacetylene, polypyrrole, polyaniline), or polyurethane or their potential copolymers. In some instances, a composition here comprise ECM and both a natural and a synthetic polymer. A composition herein can be a multi-material by linking an ECM and another polymer material, for example, via reaction with amines, free thiols, or short peptides that can be self-assembled with the ECM.

In some instances, a polymer of the composition is biocompatible and biodegradable and/or bioabsorbable, and can be a random copolymer, block copolymer or blend of monomers, homopolymers, copolymers, and/or heteropolymers that contain these monomers. Exemplary biodegradable or bioabsorbable polymers include, but are not limited to: polylactides, poly-glycolides, polycarprolactone, polydioxane and their random and block copolymers. A biodegradable and/or bioabsorbable polymer can contain a monomer selected from the group consisting of a glycolide, lactide, dioxanone, caprolactone, trimethylene carbonate, ethylene glycol and lysine. The biodegradable and/or bioabsorbable polymers can contain bioabsorbable and biodegradable linear aliphatic polyesters such as polyglycolide (PGA) and its random copolymer poly(glycolide-co-lactide-) (PGA-co-PLA). Other examples of suitable biocompatible polymers are polyhydroxyalkyl methacrylates including ethylmethacrylate, and hydrogels such as polyvinylpyrrolidone and polyacrylamides. Other suitable bioabsorbable materials are biopolymers which include collagen, gelatin, alginic acid, chitin, chitosan, fibrin, hyaluronic acid, dextran, polyamino acids, polylysine and copolymers of these materials. Any combination, copolymer, polymer or blend thereof of the above examples is contemplated for use according to the present invention. Such bioabsorbable materials may be prepared by known methods.

Therefore, methods are described herein for preparing a composition comprising decellularized ECM derived from skeletal muscle tissue. The invention also provides ECM compositions and methods derived from skeletal muscle tissue in an analogous process. Related compositions, devices and methods of production and use also are provided. In some instances a composition comprises crosslinkers including, but not limited to, common collagen crosslinkers, hyaluronic acid crosslinkers, or other protein cross-linkers with altered degradation and mechanical properties. The compositions which may include cells or other therapeutic agents may be implanted into a patient, human or animal, by a number of methods. In some instances, the compositions are injected as a liquid into a desired site in the patient.

In certain embodiments, the viscosity of the composition increases when warmed above room temperature including physiological temperatures approaching about 37° C. According to one non-limiting embodiment, the ECM-derived composition is an injectable solution at room temperature and other temperatures below 35° C. In another non-limiting embodiment the gel can be injected body temperature above about 37° C. or near body temperature, but gels more rapidly at increasing temperatures. A gel forms after approximately 15-20 minutes at physiological temperature of 37° C. A general set of principles for preparing an ECM-derived gel is provided along with preferred specific protocols for preparing gels in the following Examples which are applicable and adaptable to numerous tissues including without limitation the skeletal muscle.

Commercially available ECM preparations can also be combined in the methods, devices and compositions described herein. In one embodiment, the ECM is derived from small intestinal submucosa (SIS). Commercially available preparations include, but are not limited to, SURGISIS™, SURGISIS-ES™, STRATASIS™, and STRATASIS-EST™ (Cook Urological Inc.; Indianapolis, Ind.) and GRAFTPATCH™ (Organogenesis Inc.; Canton, Mass.). In another embodiment, the ECM is derived from dermis. Commercially available preparations include, but are not limited to PELVICOL™ (sold as PERMACOL™ in Europe; Bard, Covington, Ga.), REPLIFORM™ (Microvasive; Boston, Mass.) and ALLODERM™ (LifeCell; Branchburg, N.J.).

In some instances, the solution, gel form, and adsorbed form of the skeletal muscle extracellular matrix of the invention provide all the constituents at the similar ratios found in vivo. For therapeutic treatment, the skeletal muscle extracellular matrix of the invention can be delivered which can allow for skeletal muscle or other relevant tissue repair or regeneration. For in vitro cell culture for skeletal muscle cells and other relevant cells, the gel and adsorbed forms of the skeletal muscle extracellular matrix of the invention contain all or many of the same extracellular matrix cues that the cells recognize in vivo as compared to the commonly used collagen, laminin, SURECOAT (CELLUTRON, mixture of collagen and laminin), and gelatin.

The compositions herein provide a particulate, powder, emulsion, gel or solution form of skeletal muscle extracellular matrix, and the use of these forms of skeletal muscle extracellular matrix for skeletal muscle or other relevant tissue repair or regeneration, for treatment of certain diseases, such as PDA, CLI, pressure ulcers, venous ulcers, diabetic ulcers, chronic vascular ulcers, tunneled/undermined wounds, surgical wounds (donor sites/grafts, post-Mohs surgery, post-laser surgery, podiatric, wound dehiscence), trauma wounds (abrasions, lacerations, second-degree burns and skin tears), draining wounds, inflammation, Buerger disease, atherosclerosis obliterans, and thromboangiitis obliterans, and gangrene, or for cell culture. In one embodiment, the skeletal muscle tissue is first decellularized, leaving only the extracellular matrix. The matrix is then lyophilized, ground or pulverized into a fine powder, and solubilized with pepsin or other enzymes, such as, but not limited to, matrix metalloproteases, collagenases, and trypsin.

For gel therapy, the solution is then neutralized and brought up to the appropriate concentration using PBS/saline. In one embodiment, the solution can then be injected through a needle into the injured tissue or a tissue in need. The needle size can be without limitation 22 g, 23 g, 24 g, 25 g, 26 g, 27 g, 28 g, 29 g, 30 g, or smaller. In one embodiment, the needle size through which the solution is injected is 27 g. Delivery can also occur through a balloon infusion catheter or other non-needle catheter. Dosage amounts and frequency can routinely be determined based on the varying condition of the injured tissue and patient profile. At body temperature, the solution can then form into a gel. In yet another embodiment, gel can be crosslinked with glutaraldehye, formaldehyde, bis-NHS molecules, or other crosslinkers.

In yet another embodiment, the ECM can be combined with other therapeutic agents, such as cells, peptides, proteins, DNA, drugs, nutrients, antibiotics, survival promoting additives, proteoglycans, and/or glycosaminolycans. In yet another embodiment, the ECM can be combined and/or crosslinked with a synthetic polymer. Examples of synthetic polymers include, but are not limited to: polyethylene terephthalate fiber (DACRON™), polytetrafluoroethylene (PTFE), polylactic acid (PLA), polyglycolic acid (PGA), polyethylene glycol (PEG),), poly(ethylene glycol) diacrylate (PEG diacrylate), polyethylene, polystyrene and nitinol.

In yet another embodiment, ECM solution or gel can be injected into the injured tissue or other relevant tissue in need, alone or in combination with above-described components for endogenous cell ingrowth, angiogenesis, and regeneration. In yet another embodiment, the ECM or ECM liquid can be sprayed on or into injured tissue or other relevant tissue in need, alone or in combination with above-described components for endogenous cell ingrowth, angiogenesis, and regeneration. In yet another embodiment, the composition can also be used alone or in combination with above-described components as a matrix to change mechanical properties of the skeletal muscle or other relevant tissues and/or to restore muscle mass and function. In yet another embodiment, the composition can be delivered with cells alone or in combination with the above-described components for regenerating muscle mass and function. In yet another embodiment, the composition can be used alone or in combination with above-described components for increasing arteriole and capillary density, as well as recruiting more desired cells for tissue repair and regeneration.

In one embodiment for making a soluble reagent, the solution is brought up in a low pH, neutral pH, or physiological pH solution including but not limited to 0.5 M, 0.1, or 0.01 M acetic acid or 0.1M HCl, PBS, or other buffering solutions to the desired concentration and then placed into tissue culture plates/wells, coverslips, scaffolding or other surfaces for tissue culture. After placing in an incubator at 37° C. for 1 hour, or overnight at room temperature, the excess solution is removed. After the surfaces are rinsed with PBS, cells can be cultured on the adsorbed matrix. The solution can be combined in advance with peptides, proteins, DNA, drugs, nutrients, survival promoting additives, proteoglycans, and/or glycosaminoglycans before, during, or after injection/implantation.

The present invention provides enhanced cell attachment and survival on both the therapeutic composition and adsorbed cell culturing composition forms of the skeletal muscle extracellular matrix in vitro. The soluble cell culturing reagent form of the skeletal muscle extracellular matrix induces faster spreading, faster maturation, and/or improved survival for skeletal muscle cells and other relevant cells compared to standard plate coatings.

In an embodiment herein, a biomimetic ECM derived from native skeletal muscle tissue is disclosed. In some instances, a matrix resembles the in vivo skeletal muscle or other relevant tissue environment in that it contains many or all of the native chemical cues found in natural skeletal muscle ECM. In some instances, through crosslinking or addition or other materials, the mechanical properties of healthy adult or embryonic skeletal muscle can also be mimicked. As described herein, skeletal muscle ECM can be isolated and processed into a gel using a simple and economical process, which is amenable to scale-up for clinical translation.

In some instances, a composition as provided herein can comprise a matrix and exogenously added or recruited cells. The cells can be any variety of cells. In some instances, the cells are a variety of skeletal muscle or relevant cells including, but not limited to: stem cells, progenitors, skeletal muscle precursor cells, and fibroblasts derived from autologous or allogeneic sources.

The invention thus provides a use of a gel made from native decellularized skeletal muscle extracellular matrix to support isolated neonatal skeletal muscle or stem cell progenitor derived skeletal muscle cells in vitro and to act as an in situ gelling scaffold, providing a natural matrix to improve cell retention and muscle mass restoration. A scaffold created from skeletal muscle ECM is well-suited for cell transplantation in the injured tissue, since it more closely approximates the in vivo environment compared to currently available materials.

A composition herein comprising skeletal muscle ECM and exogenously added cells can be prepared by culturing the cells in the ECM. In addition, where proteins such as growth factors are added into the extracellular matrix, the proteins may be added into the composition, or the protein molecules may be covalently or non-covalently linked to a molecule in the matrix. The covalent linking of protein to matrix molecules can be accomplished by standard covalent protein linking procedures known in the art. The protein may be covalently or linked to one or more matrix molecules.

In one embodiment, when delivering a composition that comprises the decellularized skeletal muscle ECM and exogenous cells, the cells can be from cell sources for treating certain diseases, such as PAD or CLI, that include allogeneic, xenogeneic, or autogenic sources. Accordingly, embryonic stem cells, fetal or adult derived stem cells, induced pluripotent stem cells, skeletal muscle progenitors, fetal and neonatal skeletal muscle cells, mesenchymal cells, parenchymal cells, epithelial cells, endothelial cells, mesothelial cells, fibroblasts, hematopoietic stem cells, bone marrow-derived progenitor cells, skeletal cells, macrophages, adipocytes, and autotransplanted expanded skeletal cells can be delivered by a composition herein. In some instances, cells herein can be cultured ex vivo and in the culture dish environment differentiate either directly to skeletal muscle cells, or to bone marrow cells that can become skeletal muscle cells. The cultured cells are then transplanted into the mammal, either with the composition or in contact with the scaffold and other components.

Adult stem cells are yet another species of cell that can be part of a composition herein. Adult stem cells are thought to work by generating other stem cells (for example those appropriate to skeletal muscle) in a new site, or they differentiate directly to a skeletal muscle cells in vivo. They may also differentiate into other lineages after introduction to organs, such as the skeletal muscle. The adult mammal provides sources for adult stem cells in circulating endothelial precursor cells, bone marrow-derived cells, adipose tissue, or cells from a specific organ. It is known that mononuclear cells isolated from bone marrow aspirate differentiate into endothelial cells in vitro and are detected in newly formed blood vessels after intramuscular injection. Thus, use of cells from bone marrow aspirate can yield endothelial cells in vivo as a component of the composition. Other cells which can be employed with the invention are the mesenchymal stem cells administered with activating cytokines. Subpopulations of mesenchymal cells have been shown to differentiate toward skeletal muscle generating cell lines when exposed to cytokines in vitro.

Human embryonic stem cell derived skeletal muscle cells can be grown on a composition herein comprising the skeletal muscle ECM of the present invention. In some instances, hESC-derived skeletal muscle cells grown in the presence of a composition herein provide a more in vivo-like morphology. In some instances, hESC-derived skeletal muscle cells grown in the presence of a composition herein provide increased markers of maturation.

The invention is also directed to a drug delivery system comprising decellularized skeletal muscle extracellular matrix for delivering cells, drugs, molecules, or proteins into a subject for treating defective, diseased, damaged, ischemic, ulcer or other injured tissues or organs. In one embodiment, the inventive biocompatible skeletal muscle ECM material comprising the decellularized skeletal muscle extracellular matrix alone or in combination with other components is used for treating PAD, CLI, and other diseases to increase arteriole and capillary density and restore muscle mass and function. Therefore, the inventive biocompatible ECM material can be used to transplant cells, or injected alone to recruit native cells or other cytokines endogenous therapeutic agents, or act as a exogenous therapeutic agent delivery vehicle.

The composition of the invention can further comprise cells, drugs, proteins, or other biological material such as, but not limited to, erythropoietin (EPO), stem cell factor (SCF), vascular endothelial growth factor (VEGF), transforming growth factor (TGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), cartilage growth factor (CGF), nerve growth factor (NGF), keratinocyte growth factor (KGF), skeletal growth factor (SGF), osteoblast-derived growth factor (BDGF), hepatocyte growth factor (HGF), insulin-like growth factor (IGF), cytokine growth factor (CGF), stem cell factor (SCF), platelet-derived growth factor (PDGF), endothelial cell growth supplement (EGGS), colony stimulating factor (CSF), growth differentiation factor (GDF), integrin modulating factor (IMF), calmodulin (CaM), thymidine kinase (TK), tumor necrosis factor (TNF), growth hormone (GH), bone morphogenic proteins (BMP), matrix metalloproteinase (MMP), tissue inhibitor matrix metalloproteinase (TIMP), interferon, interleukins, cytokines, integrin, collagen, elastin, fibrillins, fibronectin, laminin, glycosaminoglycans, hemonectin, thrombospondin, heparan sulfate, dermantan, chondroitin sulfate (CS), hyaluronic acid (HA), vitronectin, proteoglycans, transferrin, cytotactin, tenascin, and lymphokines.

Tissue culture plates can be coated with either a soluble ligand or gel form of the extracellular matrix of the invention, or an adsorbed form of the extracellular matrix of the invention, to culture skeletal muscle cells or other cell types relevant to skeletal muscle tissue or other relevant tissue repair. This can be used as a research reagent for growing these cells or as a clinical reagent for culturing the cells prior to implantation. The extracellular matrix reagent can be combined with other tissue matrices and cells.

For gel reagent compositions, the solution is then neutralized and brought up to the appropriate concentration using PBS/saline or other buffer, and then be placed into tissue culture plates and/or wells. Once placed in an incubator at 37° C., the solution forms a gel that can be used for any 2D or 3D culture substrate for cell culture. In one embodiment, the gel composition can be crosslinked with glutaraldehye, formaldehyde, bis-NHS molecules, or other crosslinkers, or be combined with cells, peptides, proteins, DNA, drugs, nutrients, survival promoting additives, proteoglycans, and/or glycosaminolycans, or combined and/or crosslinked with a synthetic polymer for further use.

The invention further provides an exemplary method of culturing cells adsorbed on a decellularized skeletal muscle extracellular matrix comprising the steps of: (a) providing a solution comprising the biocompatible material of decellularized skeletal muscle ECM in low pH solution or approximately neutral or physiological pH including but not limited to, 0.5 M, or 0.01 M acetic acid or 0.1M HCl or PBS or any other buffered solution to a desired concentration, (b) placing said solution into tissue culture plates or wells, (c) incubating said tissue culture plates or wells above room temperature such as at 37° C., for between 1 hour and overnight (or at room temperature to 40° C.), (d) removing excess solution, (e) rinsing said tissue culture plates or wells with PBS, and (f) culturing cells on the adsorbed matrix. Cells that can be cultured on the adsorbed matrix comprising the skeletal muscle extracellular matrix of the invention include skeletal muscle cells or other cell types relevant to skeletal muscle repair, including stem cells and skeletal muscle cell progenitors.

Skeletal myoblasts plated on skeletal muscle matrix displayed a significant increase in i) the number of myosin heavy chain positive myotubes, ii) the number of nuclei per myotube and iii) myotube width when compared to cells plated on traditional collagen type I coated substrates. In some instances, the compositions are configured to provide the ability to reconstitute the in vivo muscle ECM. The composition may provide a tool to assess and maintain muscle and stem cell behavior in vitro similar to the native state, and may provide a tool for cell-mediated therapies in vivo.

In one instance, a method of making the composition herein comprises electrospinning. In some instances, a method herein is configured to control the nanofiber size, shape, or thickness. In some instances, contractility can be induced into the composition, for example, with cells or external pacing. Contractility can create cyclic stress to promote a more natural skeletal muscle. In some instances, cell influx and angiogenesis can be induced into the composition, for example, when the composition comprises linked groups or embedded factors, such as angiogenic factors.

In some instances, a composition herein may contain microbeads. Microbeads can be a part of the composition or delivered by the composition. Exemplary microbeads can be any variety of materials, for example, natural or synthetic. In some instances, the microbeads can have varied degradation properties or comprise, for example, MMP inhibitors, growth factors, or small molecules.

In some instances, the composition can comprise a biological group that can act as an adhesive or anchor where the composition is delivered. In one instance, a composition can be a bioadhesive, for example, for wound repair. In some instances, a composition herein can be configured as a cell adherent. For example, the composition herein can be coating or mixed with on a medical device or a biologic that does or does not comprises cells. For example, the composition herein can be a coating for a synthetic polymer graft. In some instances, the composition includes an anti-bacterial or anti-bacterial agents could be included. Methods herein can comprise delivering the composition as a wound repair device. In one instance, a composition comprises an alginate bead that is coated with an ECM composition as described herein.

In some instances, the composition is injectable. An injectable composition can be, without limitation, a powder, liquid, particles, fragments, gel, or emulsion. The injectable composition can be injected into an injured tissue or organ. The compositions herein can recruit, for example without limitation, endothelial, smooth muscle, skeletal muscle, progenitors, and stem cells.

The composition of the present invention can be developed for substrate coating for a variety of applications. In some instances, the ECM of the composition retains a complex mixture of muscle-specific ECM components after solubilization. In some instances, the coatings herein can more appropriately emulate the native muscle ECM in vitro.

In some instances, a composition herein is a coating. The coating can comprise an ECM from any tissue for example cardiac muscle, skeletal muscle, pericardium, liver, adipose tissue, and brain. A coating can be used for tissue culture applications, both research and clinical. The coating can be used to coat, for example without limitation, synthetic or other biologic scaffolds/materials, or implants. In some instances, a coating is texturized or patterned. In some instances, a method of making a coating includes adsorption or chemical linking. A thin gel or adsorbed coating can be formed using an ECM solution form of the composition. In some instances, a composition herein is configured to seal holes in the heart such as septal defects. The compositions of the present invention may be used as coating for biologics, medical devices or drug delivery devices.

The native ECM is a complex combination of fibrous proteins and proteoglycans that can affect many aspects of cellular behavior. To regenerate tissue, a scaffold should mimic this native microenvironment. The present invention, therefore, provides an injectable hydrogel derived from skeletal muscle ECM, which mimics the native biochemical cues, as well as being amenable to minimally invasive, injectable procedures, providing an advantage for treating PAD and CLI. In certain embodiments, the invention can be used as a delivery vehicle combined with cells and/or growth factors. In certain embodiments of the invention, the compositions and methods herein provide skeletal muscle ECM material as an acellular stand-alone therapy, which is used to recruit endogenous cells for neovascularization and repair. In certain embodiments, the present invention provides a porcine source of skeletal muscle matrix. Xenogeneic decellularized extracellular matrices are biocompatible upon removal of the cellular antigens, and can be utilized in the clinic for a number of surgical repair applications.

A liquid version of skeletal muscle matrix herein can form a porous scaffold upon injection, which promotes cellular infiltration to the damaged area. In certain embodiments, remnant growth factors are present. In other embodiments, remnant growth factors are not present. In methods herein, the decellularization and subsequent processing into the hydrogel form decreases the probability of the presence of remnant growth factors.

In the present invention, mitogenic properties of the degradation products of the skeletal muscle ECM material were assessed on smooth muscle cells, a relevant cell type for vascularization. The skeletal muscle matrix degradation fragments induced a higher proliferation rate compared to collagen. Extracellular matrix degradation products sometimes have mitogenic activity. The examples herein provide evidence that the injectable skeletal muscle matrix scaffold induces neovascularization in vivo.

Therefore, the ability of this present scaffold to induce neovascularization was then assessed in a rat hindlimb ischemia model compared to collagen, which is the predominant component of the skeletal muscle matrix and a commonly utilized scaffold. Not only was the vessel density higher in the skeletal muscle matrix, but there were significantly more large-diameter vessels greater than 25 μm, indicating maturation of the vasculature. Additionally, significance was seen as early as three days post-injection demonstrating the fast rate of vascularization. In PAD, the formation of new blood vessels is critical to treat the ischemic tissue. The presence of more mature vasculature indicates permanence of the formed vessels, which is important to getting a vascular supply as quickly as possible to the ischemic region, and to maintain blood flow (Banker and Goslin, 1998).

In addition to treating the ischemic environment, increasing muscle mass is beneficial in a therapy for PAD and CLI, as patients often suffer with muscle fatigue and atrophy. In certain embodiments, the liquid form of decellularized skeletal muscle, when utilized as a coating for cell culture, increased skeletal myoblast differentiation compared to collagen coatings. In certain embodiments, the composition provides tissue specific biochemical cues to recapitulate the skeletal muscle microenvironment. The invention demonstrated that the degradation products of this scaffold increased myoblast proliferation compared to collagen, which is consistent with literature demonstrating the inhibitory effect of collagen on smooth muscle cells and fibroblasts (Koyama et al., 1996; Rhudy and McPherson, 1988).

Next, the infiltration of muscle cells into the scaffold in the hindlimb ischemia model was assessed. The number of desmin- and MyoD-positive cells that were recruited into the skeletal muscle matrix scaffold was measured as compared to that into the collagen. Desmin, a muscle specific protein, confirms that the cells that infiltrated were from a myogenic origin. MyoD, on the other hand, is a specific striated muscle regulatory transcription factor, which coordinates the myogenic program in differentiating myoblasts (Kanisicak et al., 2009; Lee et al., 2000; Wada et al., 2002). The invention provides that there were a significantly higher number of muscle cell types in the skeletal muscle matrix, and that many of these cells were also proliferating. The MyoD-positive cells also indicate that immature progenitor cell types are recruited to the skeletal muscle matrix. The presence of these MyoD-positive and desmin-positive muscle cells indicate that the skeletal muscle scaffold is recruiting relevant cell types that aid in the regeneration of the damaged muscle, in addition to treating the ischemic tissue.

The present invention, thus, provides an acellular, biomaterial-only therapy for treating PAD. Previous biomaterial strategies for PAD have only utilized scaffolds to enhance cell or growth factor therapy (Doi et al., 2007; Jay et al., 2008; Kong et al., 2008; Layman et al., 2007; Lee et al., 2010; Ruvinov et al., 2010; Silva and Mooney, 2007). To increase its therapeutic benefit, the invention can be used in conjunction with cell or growth factor therapy as these components can be added to the biomaterial prior to injection. To create a material that could be easily prepared in the clinic, a method that allowed for long-term storage of the injectable skeletal muscle matrix scaffold was also developed with only sterile water required to resuspend it immediately prior to use.

The invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof. It is apparent for skilled artisans that various modifications and changes are possible and are contemplated within the scope of the current invention.

EXAMPLES Example 1 Injectable Skeletal Muscle Matrix

Skeletal muscle matrix material was derived through decellularization of porcine skeletal muscle tissue (FIG. 1A). Fat and connective tissue was removed, and the skeletal muscle was cut into ˜1 cm³ pieces, rinsed with deioninized water and stirred in 1% (wt/vol) solution of SDS in PBS for 4-5 days. The decellularized muscle was then stirred overnight in deionized water, and agitated rinses under running deionized water were performed to remove residual SDS. In addition to confirmation with lack of nuclei on H&E stained sections (not shown), the DNA content of the material was measured as 26.14±1.67 ng of DNA/mg of dry weight ECM, which confirmed decellularization. The matrix was then lyophilized (FIG. 1B) and milled into a fine particulate. At this stage the material can be hydrated and utilized for in vivo injection or it can be enzymatically digested to form a liquid (FIG. 1C). At this stage, the liquid skeletal muscle matrix can be diluted and utilized as a coating for cell culture, or can be brought to physiological pH and temperature, which triggers assembly into a hydrogel (FIG. 1D). After raising the pH of the material to 7.4 at room temperature, the material can also be re-lyophilized (FIG. 1E) for long-term storage at −80° C. The material can then be resuspended at a later date using only sterile water (FIG. 1F) and utilized for in vivo injection.

Example 2 Mitogenic Assay

Degradation products of decellularized ECMs have been previously shown to have mitogenic activity. It was examined whether the degradation products of the skeletal muscle matrix hydrogel had a mitogenic effect on cells in vitro. Proliferation of smooth muscle cells and skeletal myoblasts following exposure to either enzymatically degraded skeletal muscle ECM or collagen was assessed. Pepsin was also included as a control, as pepsin was utilized to digest the matrix material. A Picogreen assay was used to determine double stranded DNA content at days 3, 5, and 7 in culture to quantify cell proliferation. It was found that both smooth muscle cells (FIG. 2A) and myoblasts (FIG. 2B), when cultured in media containing degraded skeletal muscle matrix, had a higher rate of proliferation compared to cells cultured in media containing the same concentration of collagen. The increase in cell number was significantly greater at all time points (p<0.01). At day 3, there was a 1.85-fold increase in cell number in the skeletal muscle matrix wells compared to collagen for the smooth muscle cells, and a corresponding 2.15-fold increase with the skeletal myoblasts. There was also a 1.3 fold increase for skeletal muscle matrix wells compared to pepsin for both cell types, while the pepsin and collagen controls were not statistically different. Thus, degradation products of the skeletal muscle matrix were shown to promote mitogenic activity in both cell types in vitro when compared to collagen or the pepsin control.

Example 3 Gelation In Vitro and In Vivo

A gel form of the matrix was initially made in vitro by bringing the material (6 mg/mL) to a physiological pH and incubating the material at 37° C. After gelation, the material was tested for rheological properties where it was determined that the material had a storage modulus (G′) of 6.5±0.5 Pa. A representative trace of rheological data is shown in FIG. 3. The ability of the liquid skeletal muscle matrix to form a gel in situ were then assessed by injecting the material into a healthy rat hindlimb. For all in vivo studies, liquid skeletal muscle matrix, which had been biotinylated and re-lyophilized for storage at −80 C were utilized. Prior to injection, the material was resuspended in sterile water alone. The skeletal muscle matrix was then loaded into a syringe and injected intramuscularly into a rat hindlimb (FIG. 4A). To determine whether the skeletal muscle matrix would assemble and form a scaffold, the injection region was excised after 20 minutes. A visible gel, denoted by the white region in FIG. 4B, was observed within the muscle. Additional matrix injections were cryosectioned and stained to visualize the biotinylated matrix. The liquid skeletal muscle matrix assembled into a fibrous scaffold once in vivo (FIG. 4C). To assess the microarchitecture of the skeletal muscle matrix hydrogel, the material was injected subcutaneously, and excised after 20 minutes. Scanning Electron Microscopy (SEM) demonstrated that the matrix forms a porous, fibrous scaffold, both in vitro and in vivo, that is composed of fibers on the nano- and micro-scale (FIG. 5).

Example 4 Cellular Infiltration and Neovascularization

Upon confirmation that the material was able to assemble upon injection, the skeletal muscle matrix hydrogel were then examined in a rat hindlimb ischemia model to assess its potential for treating PAD. One week post-hindlimb ischemia, either skeletal muscle matrix or collagen was injected intramuscularly below the site of femoral artery resection. At 3, 5, 7 or 14 days post-injection, the muscle was harvested to determine cellular infiltration. The hydrogel was still present at all time points, although it had significantly degraded by day 14. At each time point, the amount of neovascularization, which would be critical to treat the ischemic tissue, as well as the number of muscle cells and muscle progenitors, which could aid in repair of the damaged tissue, were assessed.

To determine whether the acellular scaffold would support new vessel formation in vivo, smooth muscle cells in collagen (FIG. 6A) and skeletal muscle matrix (FIG. 6B) injected regions were labeled via immunohistochemistry. Arteriole density was significantly greater in the skeletal muscle matrix injection region compared to collagen at 3, 5, and 7 days post-injection (FIG. 6C), with many of the vessels having an average diameter greater than 25 μm (FIG. 6D). While not significant, there was still a distinct trend towards an increase in vasculature at day 14 following injection of the skeletal muscle matrix hydrogel. Additionally, endothelial cell infiltration was measured in collagen (FIG. 7A), and skeletal muscle matrix (FIG. 7B) injection regions. Endothelial cell density was found to be similar across all four time points, but was significantly greater in the skeletal muscle matrix injection region at 3 and 7 days post-injection (FIG. 7C).

In PAD and CLI, patients often suffer from general muscle fatigue and atrophy, and therefore, in addition to increasing vascularization, restoring muscle mass would also be beneficial. It was then determined whether muscle cells were also recruited to the injection site using staining against desmin (FIGS. 8A,B). The desmin positive cells were also co-stained for Ki67, a marker for proliferation, as denoted by the arrows in FIG. 8. The skeletal muscle matrix recruited significantly more desmin-positive cells when compared to the collagen matrix at 3, 5, and 7 days post-injection, a the trend that continued at day 14 (FIG. 8C). Moreover, the majority of cells expressing desmin also were Ki67 positive, indicating proliferating muscle cells were infiltrating the injection region (FIG. 8D). The number of Ki67 and desmin positive cells was significantly increased at 3, 5, and 7 days post-injection, with the same trend at day 14. Cell infiltration was further assessed using MyoD as a marker for the potential recruitment of activated satellite cells. There was a low number of MyoD positive cells recruited into the injection region of both materials at the examined time points; however, there was a statistically significant increase in MyoD positive cells in the skeletal muscle matrix (FIG. 9). The MyoD staining was prevalently perinuclear, which has been shown in other studies.

Example 5 Injectable Skeletal Muscle Matrix Powder

After milling, the skeletal muscle matrix powder is hydrated with sterile water, saline, or PBS and injected or implanted into the injured limb. Depending on the concentration, the injected skeletal muscle matrix can form a bolus or spread throughout the tissue. Upon implantation, the skeletal muscle ECM particulate forms a scaffold and creates degradation products that recruit endogenous cells to repair the ischemic region. These cells include blood vessels, skeletal muscle cells, and skeletal muscle progenitors. By recruiting endogenous cells for repair and regeneration, the skeletal muscle matrix particulate has to potential to treat peripheral artery disease and critical limb ischemia, and the various complications associated with these diseases.

Example 6 Materials, Methods and Discussion Decellularization of Skeletal Muscle for Matrix Preparation

Skeletal muscle from the hindleg was harvested from Yorkshire pigs, approximately 30-45 kg, immediately after sedation with a ketamine/xylazine combination (25 mg/kg, 2 mg/kg respectively) and euthanasia with beuthanasia (1 mL/5 kg). Fat and connective tissue was removed, and the skeletal muscle was cut into ˜1 cm³ pieces and decellularized. Briefly, the tissue was rinsed with deionized water and stirred in 1% (wt/vol) solution of sodium dodecyl sulfate (SDS) in phosphate buffered saline (PBS) for 4-5 days. Decellularized skeletal muscle was stirred overnight in deionized water and then agitated rinses under running DI water were performed to remove residual SDS. A sample of decellularized matrix was frozen in Tissue Tek O.C.T. freezing medium, sectioned into 10 μm slices, and stained with hematoxylin and eosin (H&E) to confirm the absence of nuclei. Following the decellularization protocol, the ECM was lyophilized overnight and milled to a fine powder using a Wiley Mini Mill. Additionally, to quantify DNA content, the DNeasy assay (Qiagen, Valencia, Calif.) was performed according to manufacturer's instructions. After extraction, the Take3 plate was used to measure the concentration of DNA using a Synergy 2 microplate reader (Biotek, Winooski, Vt.).

Preparation of Injectable Skeletal Muscle Matrix and Collagen

In order to render the decellularized extracellular matrix (ECM) into a liquid form, the milled form of the matrix was subjected to enzymatic digestion. Pepsin (SIGMA, St. Louis, Mo.) was dissolved in 0.1 M hydrochloric acid (HCl) to make a 1 mg/ml pepsin solution and then filtered through a 0.22 μm filter (Millipore, Billerca, Mass.). The ECM at a ratio of 10:1 was digested in the pepsin solution under constant stirring. After approximately 48 hours, the matrix was brought to a physiological pH in a BSL-2 safety cabinet, and then either diluted for in vitro assays or for injection. For in vitro and in vivo studies, the skeletal muscle matrix was brought to a pH of 7.4 through the addition of sterile-filtered sodium hydroxide (NaOH) and 10×PBS, and further diluted to 6 mg/ml using 1×PBS inside a BSL-2 safety cabinet.

Skeletal Muscle Matrix In Vitro Gel Characterization

Gels of the skeletal muscle matrix were formed, at a concentration 6 mg/ml for rheological characteristics and for scanning electron microscopy. Either 100 μl of matrix was pipetted into a 96 well plate (Corning, Corning, N.Y.) or 500 μl in glass scintillation vials and incubated overnight to form gels. Rheometry was conducted on the 500 μl in vitro-formed skeletal muscle matrix gels using a TA instruments AR-G2 rheometer. The gels were tested using a 20 mm parallel plate geometry with a 1.2 mm gap at 37° C. Three frequency sweeps were performed within the linear viscoelastic strain region. Samples were run in triplicate and then the values were averaged to calculate the storage modulus.

Scanning electron microscopy (SEM) was utilized to determine the microstructure of the skeletal muscle matrix gels. These gels were either formed in vivo by injecting the skeletal muscle matrix subcutaneously in a rat and excised after 20 minutes, or in vitro after incubation of the material in a 96 well plate at 37° C. overnight. The skeletal muscle matrix gels were harvested and fixed with 2.5% glutaraldehyde for 2 hours, and then dehydrated using a series of ethanol rinses (30-100%). Samples were then critical point dried and coated with iridium using an Emitech K575X Sputter coater. Electron microscopy images were taken using a Phillips XL30 Environmental SEM Field Emission microscope at 10 kV, with 242 μA and a working distance of 10 mm.

In Vitro Proliferation Assays

Primary rat aortic smooth muscle cells (RASMC) and C2C12 skeletal myoblasts were maintained on collagen coated plates and split at 1:5 every 2-3 days. Cells between passages 4 and 10 were plated at 750 cells/well in 96 well plates in growth media consisting of DMEM, 10% fetal bovine serum, and 1% pen-strep solution. Twenty-four hours later, the cells were washed with PBS to remove non-adherent cells. Digested skeletal muscle matrix and collagen were brought to a pH of 7.4, and then added to the growth media at concentrations of 0.05 mg/mL. As the ECM was enzymatically digested, pepsin was also included as a control at 0.005 mg/mL. All conditions were run in quadruplicate. Every two days, media was changed and cell proliferation was assessed using the PICOGREEN® assay (Invitrogen) per manufacturer's directions. Briefly, wells were rinsed in PBS and then incubated with 100 μL of TE buffer. After incubation for 30 minutes at room temperature followed by 5 minutes on a shaker, 100 μL of 1:200 Picogreen reagent was added. Upon covering the plates in foil and shaking them for 30 minutes, double stranded DNA was quantified using a fluorescent plate reader at 630 nm at days 3, 5, and 7.

In Vivo Gelation Test

To prepare for in vivo studies, a preliminary test was performed to ensure that the skeletal muscle matrix would be able to gel upon injection. The skeletal muscle matrix was labeled with biotin, and then injected into the hindlimbs of healthy Sprague Dawley rats. For biotin labeling, a 10 mM solution of EZ link Sulfo-NHS-Biotin (Pierce, Rockford, Ill.) was prepared and mixed with the liquid skeletal muscle matrix for a final concentration of 0.3 mg of biotin/mg matrix. The mixture was allowed to sit on ice for two hours. The skeletal muscle matrix was then frozen, lyophilized and stored at −80° C. until use. To resuspend the skeletal muscle matrix, sterile water was added at the original volume to bring the material to 6 mg/ml and vortexed. Female Harlan Sprague Dawley rats (225-250 g) were anesthetized using isoflurane at 5%, intubated, and maintained at 2.5% isoflurane during surgery. In preliminary studies, (n=2) 150 μl of skeletal muscle matrix was injected intramuscularly into healthy rats. The muscle was excised after 20 min, and fresh frozen using Tissue Tek O.C.T.

Hindlimb Ischemia Model

After confirmation of gelation in vivo, a rat hindlimb ischemia model was utilized to test the skeletal muscle extracellular matrix. Animals were placed in a supine position and hindlimb ischemia was induced by ligation and excision of the femoral artery. After ligation of the proximal end of the femoral artery, the distal portion of the saphenous artery was ligated and the artery and side branches were dissected free, and then excised. The area was sutured closed and animals were given an analgesic of 0.05 mg/kg of buprenorphine hydrochloride (Reckitt Benckiser Healthcare (UK) Ltd., Hull, England) prior to recovery from anesthesia. One week post-injury, the rats were anesthetized using 5% isoflurane, intubated, and maintained at 2.5% isoflurane for injection. Skeletal muscle matrix and rat tail collagen were biotinylated in order to visualize the injection region and 150 μl was injected intramuscularly. Injection was confirmed by a lightening of the muscle at the site of injection. Rats were sacrificed using an overdose of sodium pentobarbital (200 mg/kg) at 3, 5, 7, or 14 days post injection (n=4, except n=3 for 14 day collagen injection), and leg muscles were harvested and frozen in Tissue Tek O.C.T.

Histology and Immunohistochemistry

The excised muscle was cryosectioned into 10 μm slices. Slices were stained with Hematoxylin and Eosin every 1 mm and screened to determine the location of injected material. Adjacent slides were stained for visualization of biotin-labeled skeletal muscle matrix or collagen, to confirm the injection site. Slides were fixed in acetone, incubated with superblock buffer (Pierce), followed by 3% hydrogen peroxide (Sigma), and horseradish peroxidase conjugated neutravidin (Pierce) at room temperature. The reaction was visualized by incubation with diaminobenzidine (DAB, Pierce) for ten minutes.

Five slides evenly spaced within the injection region were then used for immunohistochemistry (IHC). Sections were fixed for 2 min in acetone and blocked with staining buffer for 1 h (2% goat serum and 0.3% Triton X-100 in PBS). Skeletal muscle sections were then assessed for vessel formation using a mouse anti-smooth muscle actin antibody (Dako, Carpinteria, Calif.; 1:75 dilution) to label smooth muscle cells. After three 5-minute washes with PBS, AlexaFluor 568 anti-mouse (Invitrogen, 1:200 dilution) was used as a secondary. Endothelial cell infiltration was assessed using FITC labeled isolectin (Vector Laboratories, Burlingame, Calif.; 1:100 dilution). Slides were then mounted using Fluoromount (Sigma). Sections stained with only the primary antibody or secondary antibody were used as negative controls. Images were taken at 100× using Carl Zeiss Observer D.1 and analyzed using AxioVision software. Arterioles were quantified with a visible lumen and a diameter≧10 μm and normalized over the injection area.

In order to assess proliferating muscle cell infiltration into the injection region, sections were stained using a mouse anti-desmin antibody (Sigma; dilution 1:100) and co-stained with a rabbit anti-Ki67 (Santa Cruz Biotech, Santa Cruz, Calif.; dilution 1:100). AlexaFluor 488 anti-mouse and AlexaFluor 568 anti-rabbit were used for secondary antibodies (1:200), followed by staining with Hoechst 33342. Slides were mounted with Fluoromount (Sigma) prior to imaging. Additionally, the skeletal muscle tissue was assessed using a rabbit anti-MyoD (Santa Cruz Biotech, Santa Cruz, Calif.; dilution 1:100), followed by AlexaFluor 488 anti-rabbit as a secondary antibody, and Hoechst 33342. Three 400× images were taken per slide and analyzed using AxioVision software. The number of desmin positive cells, and desmin positive cells that co-localized with Ki67 were counted, averaged and normalized over the area. For the tissue sections analyzed for MyoD, the number of positive cells with MyoD co-localized with nuclei were counted and averaged over the area of injection.

Statistical Analysis

All data is presented as the mean±standard error of mean. For the in vitro assays, samples were run in quadruplicate and results were averaged. Significance was determined using a one-way analysis of variance (ANOVA) with a Bonferroni post-test. A two-tailed Student's t-test was used for all other data and reported as p<0.05 and p<0.001.

In conclusion, the present invention provides an injectable skeletal muscle extracellular matrix scaffold as a new biomaterial-only therapy for treating PAD and CLI and complications associated with these diseases. The invention demonstrates that decellularized skeletal muscle ECM can be processed to form an injectable matrix material, which assembles into a porous and fibrous scaffold in vivo. The invention also demonstrates that degradation products of the material induce proliferation of smooth muscle cells and skeletal myoblasts in vitro. Furthermore, the invention provides that the injected scaffold increased neovascularization and infiltration of muscle cells within the biomaterial as compared to collagen, suggesting that it improves neovascularization in PAD, as well as treat the associated muscle atrophy. Thus, the invention provides a novel therapeutic treatment method for PAD and CLI with an injectable scaffold derived from decellularized skeletal muscle ECM.

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While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby. 

The invention claimed is:
 1. A method for treating peripheral artery disease comprising injecting or implanting in a subject with peripheral artery disease an effective amount of a composition comprising decellularized extracellular matrix derived from skeletal muscle tissue, wherein the composition does not contain hepatocyte growth factor.
 2. The method of claim 1, wherein said composition is coated on an implant.
 3. The method of claim 1, wherein said composition is delivered as a liquid or a powder.
 4. The method of claim 3, wherein said composition transitions to a gel form after delivery.
 5. The method of claim 1, wherein said composition degrades within one to three months following injection or implantation.
 6. The method of claim 1, wherein injection or implantation of said composition repairs damage to skeletal muscle tissue sustained by said subject.
 7. The method of claim 1, wherein injection or implantation of said composition repairs damage caused by ischemia in said subject.
 8. The method of claim 1, wherein said effective amount is an amount that increases blood flow, increases muscle mass, or induces new vascular formation in the area of the injection or implantation of the subject.
 9. The method of claim 1, wherein the effective amount is effective for treating at least one of the symptoms selected from the group consisting of ulcers, trauma wounds, draining wounds, inflammation, Buerger disease, atherosclerosis obliterans, thromboangiitis obliterans, and gangrene associated with peripheral artery disease.
 10. A method comprising injecting or implanting in a subject with critical limb ischemia an effective amount of a composition comprising decellularized extracellular matrix derived from skeletal muscle tissue, wherein the composition does not contain hepatocyte growth factor.
 11. The method of claim 10, where said composition is coated on an implant.
 12. The method of claim 10, wherein said composition is delivered as a liquid or a powder.
 13. The method of claim 12, wherein said composition degrades within one to three months following injection or implantation.
 14. The method of claim 10, wherein injection or implantation of said composition repairs skeletal muscle tissue damage caused by ischemia in said subject.
 15. The method of claim 10, wherein said composition transitions to a gel form after delivery.
 16. The method of claim 10, wherein said effective amount is an amount that increases blood flow, increases muscle mass, or induces new vascular formation in the area of the injection or implantation of the treated subject.
 17. The method of claim 10, wherein the effective amount is effective for treating at least one of the symptoms selected from the group consisting of ulcers, trauma wounds, draining wounds, inflammation, Buerger disease, atherosclerosis obliterans, thromboangiitis obliterans, and gangrene associated with peripheral artery disease. 